No time for commentary here, just pretty pictures of the insides and outputs of some cheap USB wall adapters.
Full Frontal Nudity
(click to zoom)
Here we see how the supply reacts going from open circuit to having a 10 ohm load resistor across it at time “T”. Gives you a nice view not only of how clean the output is in both cases, but also how it reacts to the sudden increase.
…and just for fun, here is an Amazon branded charger that came with my Kindle…
…and an Apple adapter….
Apparently clean and smooth housings produce clean and smooth output! :)